IIRC the SRX uses an updated, newer TC suspension (54886) than the slightly older SR. I'm not sure, but I seem to remember that this newer suspension doesn't work with the droop screws add-on (54638), but I might be mixing this up with something different. Cannot find what shocks are used on the SRX - 50746 are included with the SR, however.

EDIT: Apart from those two uncertainties (not even having the option to set droop by screws would be quite a let-down though, if true, as this is a major setup/tuning aid, which I'd not like to lose and I find it hard to imagine the updated suspension is so superior as to completely compensate for that), IMO the SRX seems to be a little better equipped, be it included parts or small improvements in detail (better front spool, aluminium prop shaft, speed gears, blades on DCJs and universals) - but I've seen price differences of 110€ between the two kits around here... . I sure like the small improvements on the SRX and kinda wish mine had these nifty details, but it's a TT-02 still, and I think I've sunk enough money into mine.