I live in the UK and im looking at spending around £1000 on my new amp and cab.

I'm loking at the http://www.musiccentre.co.uk/acatalog/Peavey_6505.html head

or the 5150

then a cheap cab like this http://www.guitarampkeyboard.com/en/gs-412i/387

I play metalcore/deathcore (architects, as I lay dying, all shall perish kind of thing) and am worried that these choices might not suit that style

advice please?

6505 and the 5150 are the same thing, baisically. The 6505/5150 has more gain, and more bass than the 5150 II/6505+ but the 5150 II/6505+ are more tight, have slightly less gain to reduce noise (Still have more gain than you'll ever need), and improved features.
Quote by satchgear
I tried it out in store.

Great neck, nice n light, good tuning stability. Overall a good guitar. I didn't but it cause I generally only buy guitars over a grand now.
get a randall V2 head costs around 750 but would easily be worth it
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why are you worried that the 5150/6505 might not suit styles like that?

most bands of those genres have used them at some point. bullet, machine head and trivium are a few big names who use them in their live rigs.