Hi
The list of bets is longer if your £100 lay is matched incrementally. If you log on to your Betfair account and check the list of bets there, you will see the same.
While processing speed and system spec might help some way, it is known that the program's performance can be affected by large numbers of bets having to be updated, or high numbers of markets being monitored. I think the latter is the more important one.
Depending on what your trading requirement is, here are a few general suggestions for trying to improve things:
use the latest version of the program
start monitoring markets only when needed
use triggers to adjust market refresh rates according to the number of markets being monitored
use triggers to delete non-required or settled markets
use Scheduler and Locator to load markets in batches according to the event start time
in the settings make sure Log Trigger Expressions is switched off
also try and switch off logging altogether and see if performance is better
switch off things you don't need that may be consuming data requests e.g. score, silks etc.