Windows 7 Firewall, Limit SSH Access to Ireland only

I've cygwin SSHD running on one of my windows 7 machines. I've noticed connection attempts for places all over the world. I'd rather restrict access a bit, in case they are attacking an exploitable flaw, or one of my password are too weak ( I must set up key-only login auth)

Now that Windows 7 has a much improved firewall, I can now add rules that allow inbound access to port 22 to a limited set of remote IP addresses.

To limit it to Ireland only, for example, I looked up the full range of Irish IP addresses using this site: http://www.countryipblocks.net/

Then I ran the following from the command line (run as Administrator):

netsh advfirewall firewall add rule name="SSHD IN Ireland Only" dir=in localport=22 protocol=TCP action=allow remoteip=62.9.0.0/16,62.17.0.0/16,62.40.32.0/19,62.77.160.0/19,62.231.32.0/19,....

The full list of subnets is quite long, and I don't know what is the maximum number of entries allowed. Indeed, neither do I know the performance impact on networking in general, if any, of a large number of entries. If they've built the firewall properly, the impact should be negligible on unrelated connections.