Excel stutters and freezes

[Hydroxide]

I'm running Excel (out of Office 365 Business) on an Intel Core i7 920 CPU (2.67 GHz) with 12 GB RAM.

For a client, I am analysing data that doesn't have that many columns, but all sources combined has almost 600,000 rows. Now whenever I as much as try to do something (such as opening a filter button to change the filter), Excel starts stuttering and freezing and the CPU load goes through the roof (~20%). At the same time, the task manager still shows free memory, and freeing more memory by closing the web browser didn't help at all.

There's nothing in terms of formulas in there, yet, just an ID and measurement results for several parameters for each ID. The file is 35MB large. My PC has handled files of that size and even much larger reasonably well in the past, so possibly, the problems came with an update?

I even tried repairing, then reinstalling Office, to no avail, and by now am at a loss and my client is getting a bit impatient as to when I'm done analyzing the data. 

[#2]

Save as file with F12 in Binary format, it will reduce file size almost 1/5th of what it is and try out again to work in your file...may be it will help you...

[#3]

Unfortunately, that didn't really help. Half an hour or so after clicking the button, the filter choice panel will pop up over whichever window I am in at that time, but will disappear before I can make any choice. Then, Excel will be running normally until such point I tell it to actually do something - the slightest action, even if just entering letters into a cell, will make it freeze within seconds again, giving me the hourglass and making the program unresponsive for yet another eternity...