you could always rent professional kitchen space too.

Wow, that's some cake! Agree with betteirene (as I generally do, I get the impression she's not the sort of lady who brooks much dissent...), you need to look at a Hobart.

Yeah, the Artisan, which is what I have, ain't gonna cut that, certainly not in one batch, and probably not even in multiple batches. Sometimes mine struggles with a 2 pound batch of bread dough. While I realize that's a whole lot stiffer than cake batter, I can't even envision being able to fit 25 pounds of cake batter in an Artisan bowl.

As others have said, I don't think, if this is going to be a regular project for you, that any home mixer is going to fit your needs. If you really need this much capacity routinely, your best bet would be a restaurant supply house. You can probably even find a vendor of used bakery/restaurant equipment that would be more cost-effective than purchasing new.

If it's a one-time only shot, hmmmm. Beg and borrow as many heavy-duty domestic machines as you can, and break the 25 pounds up into smaller amounts, then combine it all at the end, manually.

If this is a one time project, you could scale the recipe down and make it in batches. Otherwise you need to buy a commercial mixer capable of handling 25# of batter. The 2 mixers you referenced are too small.

@KitchenAidUSA tweeted the following: -The Professional and Artisan mixers are not capable of mixing 25 lbs of cake batter at 1 time. These are not for commercial use

I'm having a hard time envisioning a countertop mixer that would have a bowl big enough to hold 25 lbs. of batter---not even my fruitcake batter is that dense.

If I wanted to use my KitchenAid for a batter that heavy, I would use it only to mix the liquids and I would stir in the flour by hand.

The two professional kitchens I've worked in relied on Hobart machines. The company makes a commercial countertop mixer. Are you wealthy? It will cost $5,000 American plus shipping, and even then I'm not sure the mixing bowl has the capacity you'd need. A Hobart floor mixer could set you back $15,000 or more.

http://www.wasserstrom.com/restaurant-supplies-equipment/SearchCtrlCmd?storeId=10051&langId=-1&searchType=Basic&filter=&sort_results=relevance&narrowSearchTermFilterArray=&newSearch=true&stdPageSize=80&currPgNum=&searchFilter=&errorViewName=SearchResultsView&search_field=hobart+mixer&kwid=9da2e560b4534f48947147aaaeaaf500

You probably need a professional Hobart (probably at least 40-quart size) for that much batter, my KitchenAid 5.5 quart model can mix about 3 lbs of batter at a time (enough butter cake batter for 2 12" round pans.) Did you mean 2.5 lbs? In that case a 5-quart mixer should be sufficient.

I don't know about the Professional but 25 lbs of cake batter would be way too much for my Artisan model.