Prompted by this thread I set out to do some comparisons yesterday - taking the E30, the Vista HCx and (just for interest) the older Legend Cx, first to high open ground and then to the bottom of a steep wooded valley in search of really poor reception conditions. The latter was a total failure - even under dense canopy and beside a rocky escarpment, none of the GPSs had any trouble maintaining a fix, either stationary or at walking pace. (And IME, at cycling speeds the GPS generally perform better in forest, than at lower speeds). I suspect that, this far into autumn, the leaves may be quite dry (even though they still look quite green) and so not giving the testing conditions I was looking for.
So I had to fall back on comparisons indoors, where it's easy to control the amount of sky view but it isn't really quite representative of real-world conditions.
On high open ground, nearly a full hemisphere of sky -
Legend Cx, 9 satellites (ie 8 + EGNOS), 8 marked as EGNOS-corrected, 'accuracy' 6 metres.
Vista HCx, 11 sats (10+1), 10 marked as EGNOS-corrected, 'accuracy' 2 metres.
E30, 17 sats (10+1+6), 10 marked as EGNOS-corrected, 'accuracy' 3 metres.
I would suggest that 'accuracy' can only really be used as a self-reference - different units will probably use different algorithms to calculate this.
On my windowsill - facing north, but still with a very good sky view so nearly a demi-hemisphere, so to speak -
I chose a situation that was marginal for the weakest unit, the Legend Cx -
Legend Cx, 5 satellites (no EGNOS), 'accuracy' 6 metres.
Vista HCx, 9 satellites (no EGNOS), 'accuracy' 3 metres.
E30, 14 sats (8+5, no EGNOS), 'accuracy' 8 metres.
In terms of sensitivity (to GPS sats) the new E30 is a close match for the older 'H' types, in fact from continued observation of both while doing this testing, I'd say slightly better. Personally I don't see this as necessarily a good thing, but it does make for very fast start-up.
Without switching them off, I then went down to the basement, still facing north, a much more restricted sky view. Probably not even a hemi-semi-demi-hemisphere
I didn't bother to put my lovely old Cx through this torture.
In this photo, the unit on the left has a slight advantage in terms of sky view, though with this particular grouping of satellites I don't think it makes any difference.
Vista HCx, 4 satellites, 'accuracy' 12 metres.
E30, 10 sats (6+4), 'accuracy' 12 metres. Makes me suspect the 'accuracy' is being computed only from the GPS sats.
(The E30 continues to get a fix anywhere in my house, even in the middle by the chimney breast.)
Note in the picture above, the E30 shows an 'elevation' figure - on this screen this is the 'true' elevation as derived from GPS, not the barometric one - and in this example it's 25m adrift.