Just a word of advice, hearing a cab without "your" head is generally not a good thing...
I mean, cabs can sound pretty different depending on the thing you drive them with, so what you like/dislike in a cab's sound can become something different with another head. the best scenario would be hear/try head+cab together.
Again, the traynor is 2x15", I
think you'd be better off with a 2x12" or 4x10" for punky-ish stuff in the end, less muddy, but still able to go "low" (decent cabs, not crappy ones with 10"s that sound bad and tinlike).
You have no ideas on heads yet?
I do love SWR stuff (I use a 240w head with valve pre taken from a swr redhead combo from like 20 years ago), I used it with a number of cabs (a 2x12 Eden, a 4x12" Peavey beast, a 1x15" ampeg...) and always got nice sounds out of each cab.
I want a SWR Big Foot II cab now.
the main problem is that, as of now, you have 2 things to focus on:
1- HEAR what you play while you reharse with the band
2- think about your needs when playing live in clubs etc
if you have a practice space with no mics/PA wathevvvva you may need some decent power to stay on par with a PUNK drums sound and a loud guitar...
On the other hand, yes, if you're confident
in sound guys/decent "equipment" in the venues you'll be likely playing, a smaller amp (or at least one with niiiice tone at lower volumes) is a good choice...but it's a hard choice if you have no experience with bandmates yet...
so If I were you I'd wait to hear how loud the rest of the band actually is, if you have the chance to borrow some equipment to take different approaches to the situation
(say, a good combo, a decent head + cab, different "wattages", etc) , that would be a nice starting point to go on the infamous amp-search quest..
edit: not sure I'm making sense, I'm kinda multitasking with the brain between 7 different things in 3 different languages...