The Billion 7800DXL has a Broadcom BCM 6361 Chipset
The Billion BiPAC 8800NL R2 has a Broadcom BCM 63381 Chipset
The original Billion Bipac 8800NL uses BCM 63168 Chipset
The BCM 63381 used in the 8800NL R2 tends to be found in more lower budget devices. The original 8800NL uses a BCM 63168 and is IMO an excellent chipset. Every comparison I've seen between the 2 show the BCM63168 syncs higher (on VDSL2, haven't seen ADSL2 comparisons).
But my R2 is otherwise fine so far.