Help me choose an amp!

So...

I'm a gui**** who has dabbled in bass when necessary over the past three years. I picked up a cheap Rondo Music 6-banger in some naive hope that I could swiftly learn how to do fusion-y solos, and although this obviously didn't happen I've been playing it for the past few years and achieving minimal competency.

After playing another show with my cover band and not having a proper rig I've decided to buy my drummer's Mexican P-bass and a real rig. I'm looking to be able to keep pace in any realistic practice or gigging situation with this rig... eg if I'm playing to 50+ people I'll have a sub-equipped PA, etc. Thus far I've secured a SansAmp VT bass pedal and a 4x10 500W 4 ohm GenzBenz cab.

My question to you, TBers, is this... what sort of amp should I get? Since I already have what is essentially a preamp I was thinking of just buying a power amp (eg the ART SLA-2) and running it bridged into the cab, but I've seen a bunch of ~300 watt Class D amps popping up used for around $250 as well, and the convenience of 5 lbs and the flexibility of having an *actual* bass amp with compression is intriguing to me. Will a 300-ish watt amp like an Eden WTX260 be sufficient for keeping pace with a drummer and band, or should I go the power amp route? Or will this only lead to imminent disaster and should I prowl for a used 500 W Class AB amp on Craigslist for a bit?

Thanks for your insight.