Hi Mealone,
Like yourself I've been an FSX'er for ages, only came to X-Plane with version 10. I've found myself drifting back into FSX more recently when I found the Hi Memory and Quad Core FSX.cfg tweaks to make it use my newer machine.
From my own experience so far as an owner of XP-10 global, here some answers to your questions.
GRAPHICS
I've found in XP-10 ignoring the suggested 'detected' lower graphics settings and bumping it up on my quad-core Windows 7 PC; there doesn't appear to be any real jerkiness at all.
I have a GeoForce GTS 250 graphics card and 4GB of RAM.
ATC TALK
In XP-10 you must enter a flight-plan (which you have to manually calculate, no auto flight plan like FSX) in order to communicate with ATC at all.
Once you'll created a flight plan,
- you file it with the tower.
- you tune to ground who talk to you for taxing
- they hand off to the tower, you must manually retune your radio
- once airborne you must manually re-tune to approach
- then they'll track your flight eventually handing you over to approach at destination
In FSX, in flight you can bring up the ATC window and list nearest airports and request different assistance; like landing or tracking.
This kind of feature isn't present in XP-10, you can tune your comm radio to a frequency, but unless you have a flight plan;
ATC will not speak back.
FLIGHT COMPARISON
In FSX you get a lot of help with short-cut panels, in XP-10 it's much closer to the real thing. You have to set all the comm, nav and gps features in the real location in the aircraft.
For example, setting the GPS in the Cessna Skyhawk in XP-10, it is suggested you visit the Garmin website to read the genuine manual as the you operate it just like the real thing, in situ on the dashboard.
Although you can have keyboard shortcuts for everything, you can rely on a pop-up panel for things such a taxi and landing lights.
I personally think that XP-10 is model much more on actually climbing into the real aircraft and having to find the relevant controls to fly. For example, took me a while to realise the comm and nav frequencies have to be punched in on the central column panels in the 747. Unlike in FSX, where a shortcut panel saves you time.
Sometimes I like the 'realism' of XP-10, with Austin (the owner and programmer of XP-10) basing the software on his own profressional commercial piloting experience.
However, for 'pleasure flying' and sight-seeing I drift back into FSX. It's easy to jump into any aircraft, take off and simply tune your NDB or VOR to a far off point and saunter across the sky.
MAPS
I've not actually checked in the sim freezes whilst looking at the map in XP-10. But I have found the map to be little annoying for longer flight sessions.
In FSX you can hop into the aircraft at any airfield, zoom the map out to a large area and pick a far off point.
In XP-10 for speed, it only loads the map points for a smaller radius, so far off airports, VORs, NDBs are not shown on the map until your aircraft is in nearby airspace.
In XP-10 it does show on the map a bearing ROSE around your aircraft, VORs and airports. You can see at a glance a rough heading to set.
For the UK (where I'm based), there appears to be far more airfields in XP-10 than in FSX. XP-10 appears to include alot of the little flying club airstrips, which transpire to be a simple grass strip in a field.
AIRCRAFT & SCENERY
I've found looking around the web that I can't find many downloads for aircraft or scenery. Although there is an airfoil maker that ships with XP-10 for creating your own.
As for VFR scenery, I've been tempted to purchase some for the UK but seeing mixed reports that it's compatible for XP-9 and XP-10 and some people have struggled.
As for converting FSX to XP-10, not sure on aircraft; but reading instructions on converting VFR scenery from FSX... it looks very complicated needing about 3 pieces of software.
There is another tool available (WED I think?) for creating custom airport buildings and layouts.
AI TRAFFIC & AIRCRAFT
The autogen moving cars, trains and planes in XP-10 is very good. You can reduce the quantities to speed up your FPS.
There is also an option to ask AI to fly your own aircraft so you can take a wander around inside and out of your aircraft, whilst it safely fly itself.
The 'lights' is a big feature that XP-10 has over FSX.
When flying at dawn or dusk, the sky turns red, clouds illuminate according to the suns position.
Also, at night each light is individual; car, truck, plane, street light, aircraft landing and spot lights.
So you can fly a helicopter over the auto-gen traffic at night, seeing a spot light highlight at vehicle; whilst the next street light also illuminates it.
Airfield lights are much better in XP-10, from runway to taxiways.
INSTALL SIZE
XP-10 Global comes on 8 DVDs.... but the main software is on one of them. The other 7 DVDs are the scenery/airports for the entire world.
During install you can select the areas you intend to fly in.
For example, if like me you fly mainly in the UK, it'll ask you to install from DVD 1 and then maybe one or two of the other DVDs. I opted to install all 8.... and yes takes up about 50GB.
MULTIPLAY
XP-10 does have network play, but no internet based multiplay.
As XP-10 is based on a commercial basis, it has things such as using a dual screen. Instructor can use second screen to monitor and influence scenarios on the other pilot screen.
For further reading, I suggest taking a look at the XP Support page http://www.x-plane.com/support/manuals/
For me personally, I'm torn between both....
I'm currently flying more on FSX for pleasure and sight-seeing.
Then using XP-10 for around the UK and the world flight.
(but finding airports without fuel depots in XP-10, spoils the realism.... you open a pop-up menu option to reset the fuel levels)
Hope this helps....
Enjoy
Mike