No, one vbyte [vB] is equal to four weightunits [wu]. The people working on C-Lightning use "sipa" interchangeably for a weightunit.
1,000 sat/kvB = 1 sat/vB
1 sat/vB = 0.25 sat/wu
0.25 sat/wu = 250 sat/kwu
20 sat/vB = 5,000 sat/kwu
Also see: Is there a difference between bytes and virtual bytes (vbytes)?
Lightning needs very little computing resources so the hardware in use is most certainly not the issue and has very little impact at all.
The described difference in time between the sending and receiving node is normal, to be expected and cannot be changed. The reason is that the payment/routing process works by selecting a path along which HTLCs are tried ...