im close to 300lb also, and recently had Racetech redo my rear shock with Gold Valve emulators and 16.1kg rear spring. all i can say is this baby ride NICE now compared to how it did before!
its firm for riding but not overly firm. and on bumps its gives and springs back very effectivly. although i need to adjust it a little more.
over all i can say that it WAYY worth the $$
deff in the top 4 mods i have done (including detent shift kit, ECU tune, -1 Front sprocket)