Re:Switching from 5x5 to GVT
i don't recommend doing GVT for every muscle group and every session. it actually may spark some growth, since you're switching from a strength oriented plan to a more hypertrophy specific training, but you're soon going to stop progressing. progress in working weights in a 10x10rep scheme becomes almost impossible. even if u start with 3-4 sets of 10 with a heavier weight than the last time, fatigue is eventually going to kick in and it's going to look like 8,7,7,6 etc
+in time, 10x10 can leave your cns in a pretty trashed state, especially when doing compound movements, and that will further compromise gains.
another thing is that 10x10 only allows you to handle a working weight somewhere between 60-75% 1RM. IMO that's not enough variety for long term muscle gains.
i'd suggest a standard hypertrophy approcah with a wider rep range interval. you could do a gvt protocol on isolation/machine stuff every once in a while
my 2 cents