The P+1 figures are interesting.
I'm in the middle of computing the B1 and B2 values for P+1 (to go along with the B1, B2 for P-1). 1/3 of the way so far.
Both methods provide the roughly the same number of factors (where p < 2^50) and the overlap (where a specific B1,B2 would have found a factor using either method) is relatively small.
(Sticking with B2=B1*100)
228541 factors < 2^50. B1=1000 B2=100000
P-1 finds 3516
P+1 finds 3423
BOTH: 44
229376 factors < 2^50. B1=40000 B2=4000000
P-1 finds 47113
p+1 finds 45112
BOTH: 9005
However, I'm having trouble with ecm 6.0.1 which I'm using for P+1. It segfaults in step 2 whenever I use an n > 1M. Will look into this further.
More stats later when I've factored all P+1's.