HI Becki.

I'd like to explore these ideas some more.  

The thing I struggle with at the moment is the ability to create activities for users to complete that are specific to them and often repeating

Activity Assignment
Perform uses the user group hierarchies (positions and organisations) and the audience system to assign activities.  Audiences has the advantage that you can define your own rules to define dynamic audiences, so users can come and go from the audience (and thus are assigned an activity) without admin intervention. 

Repeating activities

you can configure a wide variety of ways to repeat an activity based on variety of triggers.  user is created, user enters audience, previous activity is complete etc.  We're also adding previous activity closes as a trigger for v16.  See https://help.totaralearning.com/display/TH15/Creating+performance+activities

my big ask here would be a question type within the performance activity that was a configurable table so users could log actions over a period of say a month and then submit once done (currently thins is done outside of the system on a spreadsheet).

Are you talking about retaining an asynchronous conversation?  Assuming this we think what would be ideal is the ability to record the subject and the say manager having a conversation (about e.g. 'my Goals') that then culminates in some outcome (the Goal is updated or completed etc) at the end of the review period? 

This is typically handled with an conversation thread.  Something we have developed for another product that I'm considering for performance activites.

Another good option for your conversation is Engage.  Setting up a workspace to hold the conversation.

A great example of an activity thread can be seen on Trello.

The question here is what information you want to retain as data to be used formally.  If you want to simply record the conversation, then document the outcome (say within the Goal) then this will work (if we add this feature).  If you want to retain more of the conversation as structured data, that'll require someone to transport/translate the 'outcome of the conversation' into formal content.  

I'd suggest that 'conversations that matter' are at the heart of performance management, so this in many ways is the point of all of this.