For my 1st speaker project (Celestion Ditton 66) I used basic stranded tin plated OFC from Maplins, not sure of gauge but probably between 0.5mm2 or 0.75mm2. I used it for both crossover-speaker wiring and also as point-to-point crossover links, but the latter in hindsight would have been better served by solid core wire to prevent splaying.
For my 2nd speaker project (again Celestion Ditton 66) I used Van Damme Studio Blue as I use 2.5mm2 Van Damme Studio Blue between amp and speaker. However I chose 1.5mm2 for the internals as I thought it would be easier for a novice solderer to work with. I also stripped the entire outer jacket off to shed weight and relieve strain from the driver terminals. This time I used solid core OFC for the point-to-point crossover wiring.
As for a comparison between the budget Maplins stuff and Van Damme, can't say I noticed any difference in sound TBH!
PS - I could be wrong but I think Tannoy use silver Van Den Hul for internal hook-up wire on their recent models?
PPS -
@Rockmeister, aren't your LSU crossovers already cabled up, or are you looking to upgrade them?