There is no such thing with TrueSkill. It levels you up as fast as it thinks it can validly do so.

It's a skill rating system at it's core. The ranking system is tacked on and (IMO) poorly constructed.

: I don't have any figures to back up this claim but it felt like I was
: ranking up much faster than I would have in H2/H3.

: Before I knew it I was a level 43 in BTB.

You are. BTB with individual score ranking is equivalent to 16 player FFA TrueSkill.

Rather than 'this group of 8 players beat this group of 8 players' which gives a very low amount of information per player, it says 'this player beat 15 other players.' Which is a huge amount of information - roughly equivalent to playing 15 1v1s in a row.

BTW, in the TrueSkill FAQ it says you shouldn't do this as it causes players to optimise the ranking criteria rather than the team win criteria.

: Anyway, I know it rates you based on individual performance in some gametypes
: and team in others... In individual what does it take into account?

Personal Score, only.

This includes kills, assists, sprees and style points.

: How are these weighted? Which is more important? Should I be going for more
: kills or more points? Kill with style or just...kill?

Come first by personal score. How you get there is up to you.

Note that there are no penalties for deaths or otherwise 'poor' play so aggressive styles that rack up lots of points quickly tend to do very well.