I have run my XV144 and the internal k144XV side by side on the same and different antennas (one with a mast preamp) to see if there was any performance advantage between them, and decide if I should sell my XV144 as now extra equipment.
Lots of A/B switching listening to our 2M weak signal nets and a few contests and I have concluded there is no RX performance difference to my ear, some internal spurs on the internal transverter, but nothing that affects me, and the TX power is 7Watts out internal vs 20W out on the external transverter. I have a 10W in 2M amp so 7W is good enough, and the internal covers the FM portion of the band. I also used both to drive my 903 and 1296 transverters and they both worked great.
So my XV144 external sits lonely now. Advantage goes to the Internal as I have the K144XV reflock option and the K3 hi stability TCXO option so it is dead on up to 2M.
My XV144 is usable to 148 MHz with somewhat reduced receiver sensitivity and power output dropping to 15 watts at 148 MHz, not a problem as repeaters are not weak signal communications. I've posted my results at http://www.qsl.net/kp4md/xv144.htm
73, Carol KP4MD/W6