I've often thought 4 x Borrowdale feels about right and to corroborate this my slowest time at Borrowdale (recorded last week) x 4 works out to be 21mins slower than my BG time. Where my slowest time at Wasdale (2010)x 3 works out to be 1 hour 46 minutes faster.
On both occassions I was nearly last in each race for different reasons, at Borrowdale I suffered badly with cramp and (pretty much) walked all the way from Great Gable summit.
At Wasdale it was thick clag and rain on the summit of Scafell Pike and spotting two runners with numbers and kit through the mist proceeded to have a proper ding-dong battle on the descent, only to realise on reaching the fell gate that they were in a different event and I had to walk back up to Lingmell nose to tick the check point.
I'm not sure this proves anything really, but that's my take on it.