A challenge in answering this question with some level of accuracy is that most of us have not really controlled and isolated variables. Realistically, one person really can’t serve as validation since one of the variables to be controlled would require some number of gents all participating in the study.
For instance, one person might have started off with clamping and extending together and got great results, but those might of happened anyways because of newbie potential. Another person might have added clamping in later, but their gains potential has already slowed since newbie gains are in the past. So either one of those individuals might have a different perspective on the subject, but in reality they were not participating under the same conditions.
This is the hard part about PE. It’s difficult to isolate what works best when a good gains rates might be in the neighborhood of 0.001 cubic inches per hour of PE and this rate only decreases over time. So any one person determining with certainty the impact positive or negative of combining any two or more exercises becomes difficult.
The irony is that an experienced PE practitioner has even less of a metric to base progress on since the gains rate is deteriorating.
My personal opinion is that results come from consistency, stress over time. If adding clamping to extending keeps someone coming back for more, I say go for what keeps any one of us most consistent.
With that said, I’m sure there are others that can provide you their opinions on this matter based on their experience.
Ps
I love extending, clamping, pumping and throw them all together as I please. For better or for worse:-) . But it keeps me coming back for more!