Okay guys, I mainly play as the guitarist in an acoustic band but I also play some solo slow blues stuff, mainly as a warm up act at gigs.

Currently I have a custom built 1x12 speaker cabinet loaded with a Celestion Seventy80.

What do you guys reckon my best bet would be?

Buy the Bugera V5 and use it as a combo / through the 1x12 cabinet?
Buy the Little Giant Head?

I mainly play in the style of John Mayer / SRV.
I love the blackheart stuff, so the Little Giant gets my recommendation. All of the Bugera V stuff sounds really fizzy to me. The Blackheart would definitely handle what you're trying to do.

However, if you it's just you playing and you're not trying to be heard over a band, than 5 watts would work. Just know that 5 watts isn't going to cut it if you ever try to play as a full band.

Alternatively you could try for a Fender Blues Junior. It'd do what you want perfectly, and would definitely be loud enough to use for a full band if you ever decide you want that.

Do you have a budget?
Gibson SG Special Faded
Marshall JCM2000 DSL 401
Budget of about £250 but I like the look of the Blackheart stuff. I play with a backing track so volume isn't a problem, and it all goes through a PA anyway so I could just mic it up if I ever was to play with a full band.