if your feeling really adventures you could try flashing an iMac8,1 BootROM to your iMac7,1 and see if that works
I have a good feeling it should work given how similar the 2 machines are but it does carry a higher risk of bricking the machine.
considering a logic board is £15
![Stick Out Tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
I am prepared to give it a go if you have a 8,1 20" Stock rom?
OSX Lion (System still reports it is a 400Mhz Proc
Bens-iMac:~ beneyre$ sysctl -a | grep machdep.cpu
machdep.cpu.max_basic: 10
machdep.cpu.max_ext: 2147483656
machdep.cpu.vendor: GenuineIntel
machdep.cpu.brand_string: Intel(R) Core(TM)2 Duo CPU T9300 @ 2.50GHz
machdep.cpu.family: 6
machdep.cpu.model: 23
machdep.cpu.extmodel: 1
machdep.cpu.extfamily: 0
machdep.cpu.stepping: 6
machdep.cpu.feature_bits: 3219913727 582589
machdep.cpu.extfeature_bits: 537921536 1
machdep.cpu.signature: 67190
machdep.cpu.brand: 0
machdep.cpu.features: FPU VME DE PSE TSC MSR PAE MCE CX8 APIC SEP MTRR
PGE MCA CMOV PAT PSE36 CLFSH DS ACPI MMX FXSR SSE SSE2 SS HTT TM PBE
SSE3 DTES64 MON DSCPL VMX EST TM2 SSSE3 CX16 TPR PDCM SSE4.1
machdep.cpu.extfeatures: SYSCALL XD EM64T LAHF
machdep.cpu.logical_per_package: 2
machdep.cpu.cores_per_package: 2
machdep.cpu.microcode_version: 1551
machdep.cpu.processor_flag: 3
machdep.cpu.mwait.linesize_min: 64
machdep.cpu.mwait.linesize_max: 64
machdep.cpu.mwait.extensions: 3
machdep.cpu.mwait.sub_Cstates: 51520032
machdep.cpu.thermal.sensor: 1
machdep.cpu.thermal.dynamic_acceleration: 0
machdep.cpu.thermal.invariant_APIC_timer: 0
machdep.cpu.thermal.thresholds: 2
machdep.cpu.thermal.ACNT_MCNT: 1
machdep.cpu.thermal.core_power_limits: 0
machdep.cpu.thermal.fine_grain_clock_mod: 0
machdep.cpu.thermal.package_thermal_intr: 0
machdep.cpu.thermal.hardware_feedback: 0
machdep.cpu.thermal.energy_policy: 0
machdep.cpu.arch_perf.version: 2
machdep.cpu.arch_perf.number: 2
machdep.cpu.arch_perf.width: 40
machdep.cpu.arch_perf.events_number: 7
machdep.cpu.arch_perf.events: 0
machdep.cpu.arch_perf.fixed_number: 3
machdep.cpu.arch_perf.fixed_width: 40
machdep.cpu.cache.linesize: 64
machdep.cpu.cache.L2_associativity: 24
machdep.cpu.cache.size: 6144
machdep.cpu.tlb.inst.small: 128
machdep.cpu.tlb.inst.large: 8
machdep.cpu.tlb.data.small: 16
machdep.cpu.tlb.data.small_level1: 256
machdep.cpu.tlb.data.large: 16
machdep.cpu.tlb.data.large_level1: 32
machdep.cpu.address_bits.physical: 36
machdep.cpu.address_bits.virtual: 48
machdep.cpu.core_count: 2
machdep.cpu.thread_count: 2