It's a no brainer... Pentax, but then again I have the 3.5mm, 10mm & 14mm
XW's so the 7mm & 5mm are definitely on the list. You should be able to get
the XW cheaper than that if you shop around. All my XW's cost $445.00 each.

I should also add I have tried an 8mm Radian but not the Vixen, Still I would
go for the Pentax, but then you already a Vixen LVW-5 so keeping to the
same line of ep would be something I would look for. btw, the 3.5mm XW
is my favourite Mars ep but a x2 barlow on the 7mm would give you the 3.5mm
equivilent.

regards,CS