Well... I see very often some Atom computers Win7+opencpn running even slower than my Raspi.
There are some tips to make Raspi a little faster running OpenCpn:
-Use the Raspberry pi model "B" (512 Mb Ram).
-Overclock the Raspi (don't void warranty) to 1.000 Mz.
-Put the charts folder in a different place (a pendrive) than the main SD card (improve the charts loading).
-Using openbox instead of Lxde Desktop environment.
-Adding this lines to the config.txt of the Raspi:
you may find it useful to edit your ~/.opencpn.opencpn.conf file and add values for MEMCacheLimit and/or NCacheLimit .. see opencpn.org for details.
I am using the cm93 worldwide charts and it works very useful for me, slow but useful.
When I use the vnc client with my computer it feels like slowwww. But with my Raspi it feels just the same than working directly with the Raspi, off course slow.... but functional.
And remember your little Pi will keep recording the tracks, showing your position and even sending orders to your autopilot with a very very little power consumption.
I sail in the Mediterranean, and in the summer my Navstation becomes a oven with my Net book. Now my Pi do it to me for a fraction of power an heating. Thanks Raspi...
By the other hand, the fact than the Raspberry pi works with open source software and open hardware too is a important matter to me.