Coming to a honda forum you'll get alot of people saying buy the honda, most likely.
Honestly between the two, IMO buy the GSXR. The 954 is nice but the GSXR has more positives going for it like
1. Plenty of aftermarket parts still available (Power parts to) compared to the 954
2. As mcromo said, parts are interchangeable
3. You can still find replacement parts easily, lots of them around compared to the 954. (especially if you plan on doing track days)
4. The 954 is nice, but I see the GSXR are being a upgrade compared to the older tech on the 954.
But hey, in the end it's what feels best for you!
03 DRZ 400
05 VFR 800A
05 GSXR 1000
04 Honda 919
00 Honda Shadow ACE