So let's look at Syz's stats:
http://puu.sh/pb6g6/29e7e97909.jpg
ACC 701
CRIT 740
DET 634
SKS 497
GCD 2.44
If we assume that we need to bump SKS to 750 to get that 8th GCD, that's a net difference of 253. Let's assume, for the sake of argument, that we can just transfer 253 DET to SKS:
ACC 701
CRIT 740
DET 381
SKS 750
GCD 2.35
With this change in GCD, it will take approximately one minute (62.5s = ~25 v 26 GCDs) for you to gain +1 GCD over the previous set. So, it comes down to whether or not 253 DET would give enough of a gain for 25 GCDs to give you the equivalent of +1 GCD's worth of damage. For that to be the case, we'd need 253 DET to give each of those 25 GCDs a 4% boost (since 25x4% = 100%). This would mean each single point of Determination would need to boost the damage of any given GCD by 0.015%, at least, to account for this difference.
However, if we then as well add Blood Weapon into these calculations, we have patches of 15s with 90% of our GCD and 30s with 100% of our GCD. It becomes a bit trickier to calculate, for sure, but we can estimate it by just looking at a 45s chunk. We assume that the latter gets 8 GCDs at 2.12 (16.96) while the former gets 7 GCDs at 2.20 (15.4). It's a bit tricky. In the remaining time, the 2.35 GCD player will get 14 more GCDs, ending at 47.51. 2.44 player will get exactly the same amount of additional GCDs, ending at 47.12.
Therefore, we can see that the 2.35s GCD will gain an entire GCD on the 2.44s GCD player over the course of 47-ish seconds. When 2.44 is hitting their 21st GCD, the 2.35 is hitting their 22nd 0.4s later. If we extend this, we'll see that (re-applying Blood Weapon), the 2.35 GCD player will eclipse the 2.44 GCD player at GCD number 27. When 2.35 hits their 27th (58.11), the 2.44 GCD player hits their 26th (58.12). They both started at 0, with BW starting immediately, so this can be considered to be a standing pattern going forward... more than likely.
It falls in line with the non-BW approach, with one VERY SIGNIFICANT caveat. In the case without BW, the time it takes for lower SKS to beat out higher SKS is shorter than that when BW is included - as such, it's pretty damning evidence that supports the fact that SKS and BW do not play well together. More SKS makes BW less effective. BW's existence makes SKS less effective.