I also run without a Fury generator recently (WW+RLTW+OPKS+Rend) but anyway...
Your WW after Rend should always use the OH tick frequency for the duriation of channeling until the next Rend.
RLTW while WWing is impossible to determine because WW does indeed alternate what is considered last weapon swung for RLTW (WW frequency stays the same but it changes for RLTW) - what I found out is that the game uses the aps value displayed in the character screen details for determining which weapon aps is used for RLTW.
What I mean is of course it uses the exact non-rounded value but the frequency is determined by which weapon aps was shown last before you cast Sprint.
Here´s some of the posts about the research
The last one contains the major info. My bad for not adding it to the first post for such a long time.
EDIT: added the "RLTW while channeling WW" info to the first post. I´ll retest if Rend always resets back to MH displayed aps.
EDIT2: Yep Rend always stops to swing with MH so the next WW will always tick at the OH frequency. Sprint click after Rend but before WW click should tick at MH frequency but the next Sprint frequency may change while you channel WW, depending on what weapon aps was displayed last before clicking Sprint.
This is hugely important because the majority of us utilise a fast main hand and faster off hand set-up. Using Rend can 'reset' the hand orientation and allow you to cast tornadoes from the offhand's attack speed.
The more you know!