Do we need more MPs?

I ask this question becasue the full extent of the proposed changes to constituency boundaries for the next General Election has just been analysed. Among the many consequencies – including the loss of John Greenway's Ryedale seat – is that the number of MPs will increase from 646 to 650. Can this be justified? I believe the answer is no.
Just look at the trends.
After the post-war abolition of the university seats the House of Commons had 625 MPs: this steadily increased over the next 50 years until it reached 659 in 1997 and 2001. Amazingly, the first tranche of post-devolution changes actually reduced the number of MPs elected at the last General Election to 646 but this was too good to last so the trend is back on an upward curve.
There are still huge anomalies which the Boundary Commission has failed to address this time round. For instance, why does the average English constituency have 69,934 electors while the average Welsh constitutency only have 55,640? And they have their own Assembly. I would use this as a lever to reduce the number of Welsh MPs but it could, of course, just as easily be used as an argument for increasing the number of English MPs.
The real shortcoming of this whole boundary review exercise is that it appears no-one has ever sat down and asked the obvious question: how many MPs do we need to create an efficient, modern political assembly that is effective in holding the government of the day to account? I don't know the answer to that question but it is likely to be nearer to 300 than 700. Could you imagine the huge rows if the number of seats was slashed by half?